1. Field of the Invention
The present invention relates to a dishwashing machine, and more particularly to an electric control apparatus for controlling the supply and discharge of hot water into and from a wash tank in the dishwashing machine prior to washing operation.
2. Description of the Prior Art
In a conventional dishwashing machine disclosed in Japanese Patent Laid-open Publication No. 63-264036, an electrically operated water supply valve is disposed within a water supply pipe in connection to a supply source of hot water to be opened in response to operation of a power source switch for permitting hot water supplied into a wash tank from the supply source of hot water through the water supply pipe prior to washing operation. In this kind of dishwashing machine, the hot water remained in the water supply pipe after stopping of the machine is cooled and becomes cold water. When the water supply valve is opened by operation of the power source switch to supply fresh hot water into the wash tank from the supply source of hot water, the cold water in the water supply pipe flows with the supplied hot water into the wash tank. As a result, the hot water from the supply source may not be stored in the wash tank at a high temperature suitable for washing operation of the machine.
To solve the above problem, there has been proposed an electric control apparatus for the dishwashing machine which is designed to supply hot water into the wash tank from the supply source of hot water in response to operation of the power source switch during a first predetermined time, to discharge the hot water from the wash tank upon lapse of the first predetermined time and maintain the supply and discharge of hot water during a second predetermined time and to interrupt the supply of hot water into the wash tank upon lapse of the second predetermined time and maintain the discharge of hot water from the wash tank during a third predetermined time.
In the case that a small size water heater or boiler is adapted to the supply source of hot water, however, the supply amount of hot water into the wash tank inevitably decreases. Particularly in winter, the supply amount of hot water is noticeably decreased to maintain the temperature of hot water at a high temperature suitable for washing operation. In such a case, the hot water stored in the wash tank during the first predetermined time is fully discharged in a short period of time during the second predetermined time. If the discharge pump of the dishwashing machine sucks the air from the wash tank due to shortage of the hot water stored therein in the course of lapse of the second predetermined time, the discharge performance of the pump becomes lower or ineffective. As a result, the hot water supplied from the water heater in the course of lapse of the second predetermined time is stored and remained in the wash tank at a low temperature after lapse of the third predetermined time. If in such a condition the operation switch of the machine is operated to start washing operation, the low temperature hot water remained in the wash tank is mixed with fresh hot water newly supplied from the water heater for washing. This results in poor washing of tableware racked in the machine.
If the user leaves the dishwashing machine unattended after operation of the power source switch and returns to operate the operation switch of the machine after lapse of the third predetermined time, the hot water remained in the water supply pipe will be cooled by the ambient temperature. Even if in such a condition the operation switch is operated to start washing operation of the machine, the cooled hot water in the water supply pipe will be mixed with fresh hot water supplied from the water heater for washing. This also results in poor washing of the tableware racked in the machine. To avoid such a problem, the user has to attend to the dishwashing machine until the third predetermined time lapses.